Nuclear plant operators and service companies perform in vessel visual inspections (IVVI) in conjunction with reactor refueling operations to inspect reactor components for flaws or damage to the reactor vessel and components within the reactor including submerged pipes and bores. For example, a reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has submerged bores that need to be inspected during maintenance routines. Hollow tubular jet pumps having internal bores are positioned within an annulus to provide the required reactor core water flow. During operation of the reactor, components including their weld joints within the reactor can experience inter-granular stress corrosion cracking (IGSCC) and irradiation assisted stress corrosion cracking (IASCC) which can diminish the structural integrity of the reactor components, such as jet pumps, by way of example. It is important to periodically examine the reactor core components and all welds contained therein to determine whether any cracking or failure has occurred.
The ability to accurately and quickly perform the IVVI visual inspections can impact the outage associated with the nuclear reactor. Thus, improvements to the accuracy and speed with which visual inspections can be performed can reduce the outage period and save the nuclear plant operator significant expense.
A visual inspection system typically includes one or more cameras positioned on a remotely operated vehicle that can be moved to various locations within the reactor vessel. Each camera is coupled to a video transmission system that provides an image signal to a remotely located visual display device or storage system. These visual systems are used to inspect the reactor components for damage and/or to look for debris that may have accumulated in the reactor. A number of cameras are used for various tasks including inspections of the outer surface of pipes and inner bores of pipes, apertures and bores. Generally, each visual inspection system (camera, transmission system, and display) is required to meet predefined imaging standards to ensure that the visual inspection is capable of identifying and delineating the necessary specificity in flaw and damage identification. The requirements for IVVI visual inspection systems include visual Testing (VT) standards such as a rigorous EVT-1 standard, by way of example. The EVT-1 standard provides that the imaging system be capable of resolving a 0.0005″ (½ mil) wire on an 18 percent neutral gray background. The EVT-1 standard as well as other known visual inspection standards rely on personal evaluation by an operator to ensure that the imaging system is providing the appropriate image quality to the remote display from which the inspection is performed. Any inconsistencies can result in the failure of the visual inspection system in providing an image for viewing in which the operator can identify a potential flaw or damage which can result in failure to identify such, or can require re-inspection, and therefore added time and costs for the IVVI inspection.
Several systems have been developed for performing IVVI inspection. An example of currently available systems is the Diakont D40 Camera (Diakont Advanced Technologies, San Diego, Calif.), which is considered to be state-of-the-art for visual inspection. This system uses a tube sensor that generates a monochrome image that is converted to color through the use of colored LEDs, which are used to illuminate the area under inspection in a rapid sequence. A computer program uses the colors to convert the monochrome image into color. Even though the sequencing of the colored LEDs is rapid, the cycling of the LEDs, along with the processing time, results in delays that may be manifested as blurred images when the camera is moved. This can be problematic when resolution is important for identifying small defects. Further, the use of a tube limits the size of the camera, preventing the miniaturization needed for close inspection in tightly spaced structures.
Another drawback of existing systems is that the camera sensor, whether tube or solid state (e.g., CCD, CID, CMOS), produces an analog signal that is communicated to the image processing system. The use of analog signals presents a disadvantage since the signal must be digitized within the processor, often requiring additional processing to interpret the image using statistical methods. While many such techniques can produce good results, the additional processing can produce delays that extend the time required for accurate inspection.
Accordingly, the need remains for a radiation-hardened camera that can be used for high resolution visual inspection of high radiation environments such as nuclear reactors.